1. Field of the Invention
The invention relates generally to drive mechanisms and, more particularly, to apparatus for selectively rotating a member in either of two directions.
2. Description of the Prior Art
Powered surgical instruments that rotate surgical tools are often used during the performance of orthopedic surgical procedures. For example, a powered surgical instrument is often used to rotate drill bits, wire drivers and taps. A drill bit is used to form holes in bone which receive pins or screws. A wire driver can be driven into bone and subsequently removed to create a guide passage that receives a wire which secures together fragments of shattered bone. Further, the wire driver can be left in the bone and used as a guide for a hollow drill bit, which passes over the wire as the drill penetrates the bone, or to secure together pieces of bone. The tap is used to create a threaded passage in bone.
To employ the tools described above, the powered surgical tool must be able to rotate the tool selectively in either of two directions. Commonly, the tool is rotated in a forward direction to cause the tool to enter the bone, and in a reverse direction to permit the tool to be withdrawn from the bone. Accordingly, workers in the art have developed transmissions which employ a shaft that is rotated in a single direction by a motor to rotate an output shaft selectively in either of two directions. Benjamin et al. U.S. Pat. No. 4,277,209 discloses a threading attachment having a driver that can rotate a driven shaft, to which is mounted a tap, in either of two directions. However, the actuator of the driver that couples the driver to the members which drive the driven shaft in either of two directions must rotate with the driven shaft. Therefore, the rapid reversals of the direction of rotation which are often required when using a powered surgical instrument cannot be practically achieved with the driver shown in the Benjamin et al. patent. The device disclosed in U.S. Pat. No. 4,395,240 suffers from the same deficiency.
U.S. Pat. No. 4,510,816 discloses a transmission ("the Linden transmission") that has been incorporated into a commercially available powered surgical instrument. The Linden transmission is capable of performing rapid reversals of direction of the rotation of an output shaft, but it requires manual rotation of a sleeve to effect the reversal of rotation. The common manner of rotating the sleeve requires the use of the hand of the surgeon that is not grasping the instrument, which can cause the surgeon inconvenience during the performance of an orthopedic surgical procedure.
Therefore, there exists a need for apparatus for selectively rotating a member in either of two directions which permits rapid reversals of the direction of rotation of the member and which does not require manual manipulation of a member to achieve a rotation reversal.